Patch "ASoC: rsnd: ssi: fix race condition in rsnd_ssi_pointer_update" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

ASoC: rsnd: ssi: fix race condition in rsnd_ssi_pointer_update

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
asoc-rsnd-ssi-fix-race-condition-in-rsnd_ssi_pointer_update.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jiada Wang <[email protected]>
Date: Thu, 7 Dec 2017 22:15:38 -0800
Subject: ASoC: rsnd: ssi: fix race condition in rsnd_ssi_pointer_update

From: Jiada Wang <[email protected]>

[ Upstream commit 33f801366bdf3f8b67dfe325b84f4051a090d01e ]

Currently there is race condition between set of byte_pos and wrap it around when new buffer starts. If .pointer is called in-between it will result in inconsistent pointer position be returned from .pointer callback.

This patch increments buffer pointer atomically to avoid this issue.

---
 sound/soc/sh/rcar/ssi.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

@@ -449,25 +449,29 @@ static bool rsnd_ssi_pointer_update(stru
 				    int byte)
 {
 	struct rsnd_ssi *ssi = rsnd_mod_to_ssi(mod);
+	bool ret = false;
+	int byte_pos;
 
-	ssi->byte_pos += byte;
+	byte_pos = ssi->byte_pos + byte;
 
-	if (ssi->byte_pos >= ssi->next_period_byte) {
+	if (byte_pos >= ssi->next_period_byte) {
 		struct snd_pcm_runtime *runtime = rsnd_io_to_runtime(io);
 
 		ssi->period_pos++;
 		ssi->next_period_byte += ssi->byte_per_period;
 
 		if (ssi->period_pos >= runtime->periods) {
-			ssi->byte_pos = 0;
+			byte_pos = 0;
 			ssi->period_pos = 0;
 			ssi->next_period_byte = ssi->byte_per_period;
 		}
 
-		return true;
+		ret = true;
 	}
 
-	return false;
+	WRITE_ONCE(ssi->byte_pos, byte_pos);
+
+	return ret;
 }
 
 /*

@@ -838,7 +842,7 @@ static int rsnd_ssi_pointer(struct rsnd_
 	struct rsnd_ssi *ssi = rsnd_mod_to_ssi(mod);
 	struct snd_pcm_runtime *runtime = rsnd_io_to_runtime(io);
 
-	*pointer = bytes_to_frames(runtime, ssi->byte_pos);
+	*pointer = bytes_to_frames(runtime, READ_ONCE(ssi->byte_pos));
 
 	return 0;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/asoc-rsnd-ssi-fix-race-condition-in-rsnd_ssi_pointer_update.patch